With the development of the electronics technology, diverse array of electronic devices have been developed, and have become widespread. Examples of such electronic devices include an image forming apparatuses, such as, for example, printers, scanners, facsimile machines, copiers, and multifunction peripherals, each of which forms images on paper or a recording medium.
Image forming processes utilized by these apparatuses are also diverse. Recently, the electrophotographic method has seen wide usage.
An electrophotographic image forming apparatus uses a fusing device. The fusing device provides heat and pressure using a heating roller and a pressure roller respectively in order to fix toner on paper. The adhesion of toner depends on the amount of heat supplied to the paper or to the toner, as well as the fusing temperature and pressure. That is, if the amount of heat supplied to the toner is insufficient, the toner particles may not be fully melted, and so-called a “cold-off effect,” in which the toner particles become detached from the paper and contaminate other components, e.g., belts, rollers, etc., may occur. Also, as the printing speed is made faster, the time allotted for the transfer of heat to the toner may become shorter, exacerbating the adhesion problem.
As an attempts to enhance the fusing of the toner and to increase the printing speed, internally heating of the pressure roller has been suggested. However, the thick elastic layer formed on the surface of a pressure roller makes it difficult to transfer the internally applied heat up to the surface of the pressure roller, so the thermal efficiency is low.